The invention relates to a process for the production of a pipe, the interior surface of which has been lined with a thermoplastic layer. It also relates to the pipe thus produced, to use thereof for the production of a laid pipeline, and to the pipeline thus produced. The pipeline is in particular a metal pipeline which serves for the transport of wastewater, of gas, of crude oil or other oil, of refinery products, of water-oil mixtures, of sand-water-oil mixtures or of slurries in the mining sector or of similar fluids, or for the support and lining of an oil- or gas-production well or as drilling column during borehole construction in oil fields or gas fields.
Wastewater pipelines, oil pipelines or gas pipelines, or pipelines which transport similar fluids, have a limited operating time. The cause of this is firstly progressive corrosion damage and secondly the continuous mechanical stresses that arise during the transport of abrasive fluids. The pipelines concerned are generally at a depth of about 1 m or more on land or under water in oceans and other large bodies of water, i.e. in locations where replacement of the pipelines would be possible only at considerable cost. Metallic pipelines are often also used for stabilization and lining of boreholes in oil fields and gas fields. These pipelines, known by persons skilled in the art as casings, likewise have exposure to conditions that are highly corrosive, and also sometimes abrasive. Metallic pipelines are moreover also often used as drilling columns during borehole construction on land. These boreholes serve to provide access to sources of oil, of gas or of water. The drilling column guides the drill head during drilling. The column here is often a pipe with a cross section that permits passage of process fluids, and also of the first recovery fluids. Again, these pipelines have exposure to fluids that are highly corrosive and sometimes abrasive. There is therefore a need for pipelines that are resistant to corrosion and to abrasion.
The pipelines concerned are often equipped with a liner at the factory or for example on what are known as spool bases. The liner serves inter alia for protection from damage by corrosion. Oil-conveying pipelines are for example assembled on land prior to insertion into the ocean on what are known as spool bases, and equipped with a liner. Pipelines for casings of boreholes are provided with a liner at the factory and then inserted into the borehole.
DE 27 04 438 A1 proposes that a flexible polyethylene pipeline is inserted into the interior of outflow pipes and that the external diameter thereof is smaller than the internal diameter of the outflow pipe, where the flexible pipeline is arranged with separation from the outflow pipe, with formation of an annular space. In this process, the annular space is filled with a low-viscosity hardenable casting composition, For example magnesium cement is used as fill composition for the annular space. WO 2008/019946 describes a similar procedure.
WO 93/21398 and WO 93/21399 disclose lining systems with respectively two polyethylene inliners. The interior inliner has elevations which serve as spacers.
WO 96/06298 moreover teaches that a polyethylene or polypropylene inliner can be inserted into pipelines and, respectively, pipes provided with spacers and that the intervening space can then be filled with a hardenable composition or with a plastics material that hardens. A primer is recommended in order to improve the adhesion of this plastics material and the inliner.
Suitable processes for the insertion of an overdimensioned inliner into a pipe or a pipeline are described in Patent Applications: EP 0 562 706 A2, EP 0 619 451 A1, WO 95/27168, WO 98/02293, WO 01/16520, WO 2007/023253, EP 0 377 486 A2, EP 0 450 975 A2, EP 0 514 142 A2 and WO 96/37725.
According to these references the external diameter of the pipe inliner is designed to be somewhat larger than that of the pipe to be lined. In order to insert the inliner, the cross section thereof is then reduced by stretching, compression or folding. After the insertion of the inliner, recovery forces cause the inliner to come into contact with the internal wall of the pipe. This process can be assisted by application of pressure and heat. The pipe thus lined has no annular space. However, microscopic cavities remain, due to irregularities of the interior surface of the pipe or of the pipeline, present for example because of surface roughness, or else because of welds.
An example of a suitable insertion process is Swagelining™. In this process, once inliner pipes have been butt-welded to give a section that is somewhat longer than the carrier-pipe section to be renovated, the inliner section is drawn through a swage which temporarily reduces the diameter of the pipe. This therefore allows the inliner to be pulled into the smaller space within the carrier pipe. Once all of the inliner has been pulled into the pipeline, the tensile force is removed. By virtue of the recovery behaviour of the thermoplastic material, the inliner strives to regain its initial diameter, until it is in firm contact with the internal wall of the pipeline. This gives high wall friction between inliner and pipeline, leading to positional stabilization of the inliner and preventing longitudinal expansion induced by fluid-swelling or by the effect of heat, in excess of the expansion of the pipeline. The contact between the inliner and the internal surface of the pipe is moreover so tight that the resultant volume within the annular space is very small.
Another conventionally known insertion process is the Rolldown® process. Here again, inliner pipes are first bonded in situ by the butt-welding process. In order to permit insertion, the cross section of the inliner is reduced in the Rolldown machine with the aid of rollers arranged in pairs. The velocity of the deformation process is typically from one to three meters per minute. After insertion, the pipe ends are sealed and water pressure is applied to the inliner. This causes it to expand again to its original diameter and to establish tight contact with the internal wall of the pipe. In comparison with Swagelining, tensile forces required during the insertion of the inliner are smaller, thus reducing the stress to which the material is exposed and permitting higher insertion velocities.
These methods can also be used for insertion of the inliner at the factory.
EP 0 377 486 A2 describes the folding process.
WO 2011/042732 describes another process for the insertion of inliners with diameter greater than, or identical with, that of the carrier pipeline, wherein an inliner can be inserted into short pipe sections. According to this method the inliner is inserted into the carrier pipe through a swage.
The insertion processes described above are suitable for use of liners made of thermoplastic materials, to line pipes which serve for the transport of heating mediums, of fresh water, of wastewater, of gas, of crude or other oil, or of similar fluids, for the support and lining of oil- and gas-production wells, or as drilling columns during borehole construction in oil fields and gas fields.
All of the conventional processes described have the disadvantage that gases can permeate through the inliner. Gas therefore enters into the cavities and/or microcavities located between the inliner and the carrier pipeline. The gas pressure of the cavities is in equilibrium with the partial pressure of the gas in the conveyed fluid. In the event of pressure variations in the line, the gas located in the annular space can expand and in the worst case, the gas can assume a volume which can lead to radial contact between parts of the interior layer of the liner. This leads to blockage of the cross section of the pipe and, in the worst case, prevents any further passage of the fluid conveyed. This type of failure is known to the person skilled in the art as collapse and is the predominant type of failure of inliners. These pipes are in particular used for the conveying or transport of crude oil or natural gas or for the transport of supercritical CO2 especially under conditions where relatively rapid pressure changes are likely to occur. Pressure changes of this type are a phenomenon known in the oil and gas industry as “Rapid Gas Decompression” (RGD).
Methods of handling such pressure changes are therefore required in tertiary mineral oil production. Tertiary oil production uses supercritical CO2 as solvent for residual oil, reducing its viscosity and facilitating extraction from the oil-bearing strata. The critical temperature for CO2 is 31° C., the critical pressure being 73.8 bar. In practice, markedly higher pressures are used, since the solvent power of supercritical CO2 increases with pressure. Typical pressures are in the range from 75 to 220 bar, and the temperature associated with these pressures can be up to 150° C.
The pipes which transport supercritical CO2 often have a polymeric inliner in order to protect the usually metallic structure from corrosion. In the case of transport pipes, the liner is usually composed of polyethylene; however, it may also be composed of polyamide or of PVDF.
Rapid pressure changes may moreover occur during the operation of crude-oil pipelines and gas pipelines when the line is depressurized for maintenance operations and pressured operations, with a sudden pressure decrease. A sudden pressure decrease can also occur in such conveying pipelines, collection pipelines or transport pipelines in the event of an emergency shutdown.
The object of the invention consists in avoiding the disadvantages described and providing a process for producing a lined pipe which firstly comprises the good characteristics of the liner technologies conventionally used and secondly eliminates cavities and microcavities, so that the difficulty described above no longer arises.